Direct Measurement of Muonium 1S-2S Frequency: UHV vs 1 atm – Gas-Effect Precision Test V.2

Compare muonium 1S-2S transition (244 nm two-photon excitation (Forgive the typo in the file/manuscript at the "abstract" on this)), approx 2455 MHz) in UHV (≤10⁻¹² torr) vs 1 atm air. Target shift: ≥10⁻¹⁰ Hz (fractional 3.5 × 10⁻¹⁶). Method: split-beam interferometry + lock-in phase detection. Use PSI Mu-MASS or J-PARC—frequency combs, gas injection. Minimize collisions/thermal by quadratic extrapolation + UHV isolation. Raw results only—no QED models. If shift appears: gas density effect. Null: validates current extrapolations.